What to avoid eating before glucose test?

If you’ve ever been scheduled for a glucose test, then you know that it’s one of those times where what you eat matters a lot. Your doctor will require that you fast before the test so they can determine how well your body processes sugar. Failure to fast or eating the wrong type(s) of food could skew your results and lead to problems with your medical diagnosis. In this article, we will explore some foods and drinks you should avoid before going for a glucose test.

Why is fasting important before taking a glucose test?

Before diving into what not to eat before undergoing a glucose test, let’s quickly look at why fasting is essential in the first place. When we eat foods containing carbohydrates such as bread or sugary drinks like soda, our bodies break them down into glucose (a form of sugar). Insulin, which is produced by the pancreas gland helps move this sugar from our bloodstream into our cells where it’s used for energy.

When someone has high levels of blood sugars repeatedly over time due to insulin resistance or inadequate production -like in diabetes- several negative health effects arise such as kidney disease/poor wound healing, increased cholesterol build-up/calcified artery formation leading to heart issues among many others.

Any interfering factors like incomplete overnight water-only fasting affect an accurate diabetes diagnosis; hence pretest preparation with following dietary restrictions is necessary.

Foods and Drinks You Should Avoid Before A Glucose Test

Caffeinated Beverages

While caffeine keeps us awake when we’re feeling sleepy butt imbibing caffeinated beverages (coffee/tea/energy drinks), even decaf varieties- anytime within 8 hours prior won’t help keep those numbers down albeit they really seem tempting!

Molecules called ‘adenosine receptors’ are blocked by consuming caffeine which causes relaxation during drowsiness; still scientists believe it interferes gluconeogenesis-related hormone epinephrine’s action hence compromises glucose regulation consequently can lead to high sugar levels artificially. Try settling for herbal teas or water instead.


Thinking of eating your favorite bowl of pasta for dinner the night before the test? Think again! Pasta, rice, bread, cereals and candy are all carbohydrate-heavy foods that could skew the results from your blood tests:

  • Rice: It has a lot of carbohydrates which increases insulin secretion leading to glucose tolerance impairment before testing

  • Cereals: Most cereal boxes indicate how healthy their product is but– What they don’t tell you is just how much it’ll interfere with your test results after consuming highly processed grains made quick absorbance in the body raising sugar levels more than required.

  • Pro-tip: Bowl of oats/oatmeal prepared with water/milk consist slow-releasing carbs; however using fruit/honey/sugar may spike up postprandial (post-meal) blood sugars!

In essence,you should avoid starch-rich meals/dishes for three days pre-test day because carb loading diets stimulate insulin intake rates leaving little transparency behind our natural glucose metabolism.


The act chewing leads to an increase in saliva content and endorphin release -a.k.a runner’s high-. However added sweeteners being taken [even when fasting] will affect salivary production thereby affecting artificial sweetener-mimicked glucagon-like peptide 1 also known as incretin hormones causing immediate rise in insulin levels altering diagnostic measurements significantly

Beware the ‘sugar-free’ warning signs on those packets/labels that appears harmless at first glance!


Majority believe having protein-based/fatty varieties won’t sway lab reports strictly speaking…but one essential amino acid stands out as concerning : Leucine -mostly found in red meats like beef/chicken- normally raises serum human growth hormone secretion coincidentally, surging blood sugars along with increased gluconeogenesis (glucose production especially in absence of carbs).

Alternatively, stick to ‘lean’ proteins like fish, eggs and beans 3 days prior.


When our bodies metabolize alcohol content – which as per the American Diabetes Association could only be consumed occasionally/drunk under strict medical/supervisory guidance- mobilizes glucose from liver leading to hypoglycemia; however prior intake alters insulin release/action rhythm causing sugar spikes alongside interruption of conversion.

It’s safest not to drink any alcoholic beverages within a 24-hour window preceding your test date if testing for diabetes or insulin resistance.


Before anyone pokes fun for including fruits in list make note that while oddly rare, consumption of certain fruits before taking part can seriously multiply readings on lab reports! Because it habitually contains natural sugars called fructose followed by its quick absorption through small intestine absconds necessity for pancreatic contribution hence revving up liver metabolic functions:

  • Grapes contain huge amounts of sugar in comparison to other trending fruit variants thereby making their effect worse on diabetic readings directly affecting blood circulation.

-Citrusy delights: Orange family has an impact similar grapes although they contain citrates [related organic acids]- affecting performance of some tests even besides GTT evaluations

In view avoid consuming sweet-fruits entire day pre-test unless advised otherwise because excessive fast-absorption-type carbohydrates ruin accuracy during results interpretation phase


Now you know what foods not to eat before a glucose tolerance test. Healthy diets raise metabolism ensuring good routine bodily function(s); but when specified testing requirements surfaces concerning dietary changes such as complete overnight water-only fasting followed by low-carb diet restriction spanning several consecutive days so one should ensure sticking up performing better than just common standards!

To summarize, staying hydrated with plain water is essential during this period without any solids/diuretic liquids will prove useful (especially when dealing with type 2 diabetes) in getting an accurate result. While it’s okay to indulge occasionally or have diets comprised of variety and moderation, but strictly following medically mandated rules implemented during periods like prior testing eventually benefits the health management process overall!

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